Optical element positioning apparatus, projection optical system and exposure apparatus

ABSTRACT

An optical element is moved in six-degrees-of-freedom. Three first displacement sensors are disposed on a base plate and measure respective displacement amounts of three mutually different points on the optical element in a first direction. A second displacement sensor measures a displacement amount of one point on the optical element in a second direction. Two third displacement sensors measure respective displacement amounts of two mutually different points on the optical element in a third direction. A transformation processor transforms the six measured displacement amounts. A calibration processor calibrates the transformed displacement amounts with a calibration matrix of which coefficients are previously obtained to calibrate the displacement amounts in the six-degrees-of-freedom, which have errors due to measurement errors of the displacement sensors. A controller outputs command values based on differences between the calibrated displacement amounts and target displacement amounts.

This application is a divisional of copending U.S. patent applicationSer. No. 12/171,644, filed on Jul. 11, 2008, and published as U.S.Patent Application Publication No. 2009/0021847 A1 on Jan. 22, 2009.

This application claims the benefit of Japanese Patent Application No.2007-186924, filed on Jul. 18, 2007, which is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to an optical element positioningapparatus that performs positioning of an optical element suitable for,for example, an exposure apparatus used in a lithography process of adevice manufacturing process.

Semiconductor devices, such as semiconductor memories and logic circuitswith a minute circuit pattern, are manufactured using a photolithography(exposure) technique. For this purpose, conventionally, a reductionprojection exposure apparatus is used. The reduction projection exposureapparatus projects a circuit pattern drawn on a reticle (or mask)through a projection optical system onto a substrate, such as a wafer,to transfer the circuit pattern thereon.

A minimum dimension (resolution) transferable with the reductionprojection exposure apparatus is proportional to a wavelength of lightused for exposure, and inversely proportional to a numerical aperture(NA) of the projection optical system. Accordingly, a shorter wavelengthresults in a higher resolution. Consequently, in order to satisfy therecent need for miniaturization of semiconductor devices, the wavelengthof the exposure light is being reduced. For example, as a light sourceof ultraviolet light, an ultra-high pressure mercury lamp (i-ray(wavelength: approximately 365 nm)), a KrF excimer laser (wavelength:approximately 248 nm) or an ArF excimer laser (wavelength: approximately193 nm) is used.

However, since the miniaturization of semiconductor devices isprogressing rapidly, there is a limit in the lithography usingultraviolet light. In order to efficiently transfer extremely minutecircuit patterns on the order of 0.1μ or less, a reduction projectionexposure apparatus, which uses an extreme ultraviolet ray (EUV)(hereafter, referred to as an EUV exposure apparatus), has beendeveloped. The wavelength of the extreme ultraviolet ray (EUV) isapproximately 10 to 15 nm, which is further shorter than that of theultraviolet light.

To achieve a high resolution exposure, the position and posture ofoptical elements, such as mirrors and lenses located within theprojection optical system, have to be precisely measured, and theoptical elements have to be positioned so that the wavefront aberrationfalls within a permissible value. To precisely measure the position andposture of the optical elements, for example, laser gaugeinterferometers, mounted on a measuring frame, whose installationsurfaces are satisfactorily prevented from vibrations and which has asatisfactory rigidity, are desirably used. However, due to the actualdisposition of the laser gauge interferometers, it is extremelydifficult to measure the position and posture of the optical elementsdisposed within an optical element holding barrel of the projectionoptical system, from such a measuring frame.

Japanese Patent Laid-Open No. 2005-175177 discloses a method in whichlaser gauge interferometers are mounted on an optical element holdingbarrel, and the movement amount of optical elements (mirrors) ismeasured.

Japanese Patent Laid-Open No. 2006-250587 discloses a measuringapparatus in which first and second sensors are provided, whosemeasurement axes are previously adjusted in a first axial direction anda second axial direction, respectively. The measuring apparatus isprovided with the first and second sensors (three for each) between aninner ring and an outer ring. Thereby, relationships in positions andpostures of the inner ring and the outer ring in directions of X, Y, Z,θx, θy, θz are calculated.

When the laser gauge interferometers are mounted on the optical elementholding barrel as disclosed in Japanese Patent Laid-Open No.2005-175177, mounting errors of the laser gauge interferometers causeAbbe errors, which cause errors in measurement results of the movementamounts of the mirrors. To reduce the measurement errors due to themounting errors of the laser gauge interferometers, the positions of thelaser gauge interferometers mounted on the optical element holdingbarrel and the spans between the laser gauge interferometers have to beprecisely obtained. However, it is extremely difficult to preciselyobtain the positions of the laser gauge interferometers mounted on theoptical element holding barrel and the spans therebetween.

Even when the measuring apparatus is used, in which the first and secondsensors, whose measurement axes are previously adjusted in the first andsecond axial directions, as disclosed in Japanese Patent Laid-Open No.2006-250587, a measurement error caused from the mounting error of themeasuring apparatus cannot be prevented.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an apparatus that precisely positions anoptical element in six-degrees-of-freedom (that is, in six freedomdirections).

The present invention provides, according to an aspect thereof, anapparatus that includes an optical element and positions the opticalelement. The apparatus includes a holder configured to hold the opticalelement, a back plate configured to support the optical element via theholder, a mechanism configured to move the optical element insix-degrees-of-freedom, a base plate configured to support the backplate via the mechanism, three first displacement sensors disposed onthe base plate and configured to measure respective displacement amountsof three mutually different points on the optical element in a firstdirection, a second displacement sensor disposed on the base plate andconfigured to measure a displacement amount of one point on the opticalelement in a second direction different from the first direction, twothird displacement sensors disposed on the base plate and configured tomeasure respective displacement amounts of two mutually different pointson the optical element in a third direction different from the first andsecond directions, a transformation processor configured to transformthe six displacement amounts measured by the first, second and thirddisplacement sensors into displacement amounts of the optical element inthe six-degrees-of-freedom, a calibration processor configured tocalibrate the displacement amounts transformed by the transformationprocessor, and a controller configured to output command values to themechanism based on differences between the displacement amountscalibrated by the calibration processor and target displacement amountsof the optical element.

The present invention provides, according to another aspect thereof, anapparatus that includes an optical element and positions the opticalelement. The apparatus includes a holder configured to hold the opticalelement, a back plate configured to support the optical element via theholder, a mechanism configured to move the optical element insix-degrees-of-freedom, a base plate configured to support the backplate via the mechanism, three first displacement sensors disposed onthe base plate and configured to measure respective displacement amountsof three mutually different points on the back plate in a firstdirection, a second displacement sensor disposed on the base plate andconfigured to measure a displacement amount of one point on the backplate in a second direction different from the first direction, twothird displacement sensors disposed on the base plate and configured tomeasure respective displacement amounts of two mutually different pointson the back plate in a third direction different from the first andsecond directions, a transformation processor configured to transformthe six displacement amounts measured by the first, second and thirddisplacement sensors into displacement amounts of the optical element inthe six-degrees-of-freedom, a calibration processor configured tocalibrate the displacement amount transformed by the transformationprocessor, and a controller configured to output command values to themechanism based on differences between the displacement amountscalibrated by the calibration processor and target displacement amountsof the optical element.

The present invention provides, according to still another aspectthereof, a projection optical system including the above apparatus, anda structure configured to support the apparatus.

The present invention provides, according to yet still another aspectthereof, an exposure apparatus including the above projection opticalsystem. The exposure apparatus exposes a substrate with light via theprojection optical system.

The present invention provides, according to still another aspectthereof, a method of manufacturing a device, including the steps ofexposing a substrate using the exposure apparatus, developing theexposed substrate, and processing the developed substrate to manufacturethe device.

Other aspects of the present invention will be apparent from theembodiments described below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically illustrating the configuration of aprojection optical system that is Embodiment 1 of the present invention.

FIG. 2 shows a top view and a side view schematically illustrating theconfiguration of an optical element positioning apparatus of Embodiment1.

FIG. 3 is a flowchart of a calibration process in Embodiment 1.

FIG. 4 is a flowchart of an adjustment process of wavefront aberrationin Embodiment 1.

FIG. 5 shows a top view and a side view schematically illustrating theconfiguration of an optical element positioning apparatus that isEmbodiment 2 of the present invention.

FIG. 6 is a block diagram illustrating a control method of the opticalelement positioning apparatus of Embodiment 1.

FIG. 7 shows a top view and a side view illustrating the configurationof a calibrator in Embodiment 1.

FIG. 8 is a block diagram illustrating a measurement-informationprocessing method in the calibrator shown in FIG. 7.

FIG. 9 is a block diagram illustrating a control method of the opticalelement positioning apparatus of Embodiment 1.

FIG. 10 illustrates a calibration matrix in Embodiment 1.

FIG. 11 illustrates the calibration matrix in Embodiment 1.

FIG. 12 illustrates an exposure apparatus that is Embodiment 3 of thepresent invention, to which the optical element positioning apparatus ofEmbodiments 1 and 2 is applicable.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the accompanying drawings.

Embodiment 1

While taking an EUV exposure apparatus as an example, an optical elementpositioning apparatus and a projection optical system mounted therewith,each of which is a first embodiment (Embodiment 1) of the presentinvention, will be described below.

In many cases, a projection optical system, which is mounted on an EUVexposure apparatus, is constituted by six or eight optical elements(mirrors). In Embodiment 1, a description will be made of a projectionoptical system that includes an optical element holding barrelcontaining six optical elements 1 (1_m1 to 1_m6), as shown in FIG. 1.

The optical elements 1 (1_m1 to 1_m6) are respectively mounted onoptical element positioning apparatuses 7 (7_m1 to 7_m6). A projectionoptical system 101 is constituted by mounting the optical elementpositioning apparatuses 7 on an optical element holding barrel 100.

FIG. 2 illustrates the configuration of one of the optical elementpositioning apparatuses 7. The optical element positioning apparatus 7performs positioning of the optical element 1 in six-degrees-of-freedomin an orthogonal coordinate system, with respect to a base plate 5.

As shown in FIG. 2, a back plate 3 supports the optical element 1through a holding mechanism 2. The base plate 5 supports the back plate3 through position adjusting mechanisms 4 (4_1 to 4_6), which aredisplacing mechanisms.

Each of the position adjusting mechanisms 4 uses a parallel linkmechanism. The parallel link mechanism includes a Stewart platform type,a direct acting type and a rotational type. Any one of the above typesmay be employed.

Each of the position adjusting mechanisms 4 (4_1 to 4_6) is providedwith actuators. The actuators are capable of moving the optical element1 in six-degrees-of-freedom (that is, in six freedom directions). Apiezoactuator, a Pico motor, or the like, may be used as the actuator.

In Embodiment 1, each of the position adjusting mechanisms 4 employs theparallel link mechanism. However, if the positioning is possible freelyin the six-degrees-of-freedom, a positioning mechanism using a linearmotor may be employed.

The base plate 5 is provided with displacement sensors 6 (6_X1, 6_Y1,6_Y2, 6_Z1, 6_Z2, 6_Z3), each of which measure a displacement amount ofthe optical element 1. A displacement sensor as a Michelsoninterferometry technique, a linear encoder, a capacitance sensor, or thelike, which provides a satisfactory measuring accuracy and measurementrange, may be used as each of the displacement sensors 6.

The displacement sensor 6_X1 measures a displacement amount ΔX1 of theoptical element in an X-axial direction with respect to the base plate5. The displacement sensor 6_Y1 measures a displacement amount ΔY1 ofthe optical element 1 in a Y-axial direction with respect to the baseplate 5. The displacement sensor 6_Y2 measures a displacement amount ΔY2of the optical element 1 in the Y-axial direction with respect to thebase plate 5.

The displacement sensor 6_Z1 measures a displacement amount ΔZ1 of theoptical element 1 in a Z-axial direction with respect to the base plate5. The displacement sensor 6_Z2 measures a displacement amount ΔZ2 ofthe optical element 1 in the Z-axial direction with respect to the baseplate 5. The displacement sensor 6_Z3 measures a displacement amount ΔZ3of the optical element 1 in the Z-axial direction with respect to thebase plate 5.

The displacement sensors 6_Z1, 6_Z2 and 6_Z3 are three different firstdisplacement sensors, which measure displacement amounts of three pointsdifferent from each other in the optical element 1 in the Z-axialdirection (first direction). The displacement sensors 6_X1, 6_Y1 and6_Y2 are three second displacement sensors, which measure displacementamounts of three points different from each other in the optical element1 in the X-axial direction and the Y-axial direction (in two directionsdifferent from the first direction and from each other).

The measurement information (ΔX1, ΔY1, ΔY2, ΔZ1, ΔZ2, and ΔZ3) obtainedby the respective displacement sensors 6 is hereafter referred to asmeasurement information 31 of the displacement sensors 6.

Referring to FIG. 6, a positioning control method of the optical element1 will be described below.

The measurement information 31 of the displacement sensors 6 istransformed into movement amounts (displacement amounts) (ΔX, ΔY, ΔZ,Δθy, and Δθz) by a movement amount transforming matrix (transformingprocessor) 21. The movement amounts (ΔX, ΔY, ΔZ, Δθx, Δθy and Δθz)represent movement amounts of a control center of the optical element 1in the six-degrees-of-freedom in the orthogonal coordinate system of thebase plate 5. The movement amount transforming matrix 21 holdsinformation on a positional relationship between the control center ofthe optical element 1 and the displacement sensors 6, and information ona mounted angle of each displacement sensor 6. The movement amounts (ΔX,ΔY, ΔZ, Δθx, Δθy and Δθz) of the control center of the optical element 1in the six-degrees-of-freedom in the orthogonal coordinate system of thebase plate 5 are hereafter referred to as movement amounts 32 of theoptical element 1. The movement amounts 32 of the optical element 1 areinput to a difference calculator 27.

The difference calculator 27 calculates control deviations 34 (ErrX,ErrY, ErrZ, Errθx, Errθy and Errθz) of the optical element 1 in thesix-degrees-of-freedom, as described below. That is, differences betweenthe movement amounts 32 ((ΔX, ΔY, ΔZ, Δθx, Δθy and Δθz) of the opticalelement 1 and target movement amounts 30 (ΔXr, ΔYr, ΔZr, Δθxr, Δθyr andΔθzr) of the optical element 1 are calculated to obtain the controldeviations 34.

A control compensator 23 includes a PI compensator or a PID compensator,a notch filter, and a low-pass filter, and the like. The controlcompensator 23 calculates driving force information 35 (ΔFx, ΔFy, ΔFz,ΔTx, ΔTy and ΔTz) of the optical element positioning apparatus in thesix-degrees-of-freedom, which are according to the control deviations34.

An output distribution matrix 24 includes a transforming matrix thattransforms the outputs from the position adjusting mechanism 4 intomovement amounts of the optical element 1 in the six-degrees-of-freedom.The output distribution matrix 24 calculates command values for thefollowing position adjusting mechanisms 4, based on the driving forceinformation 35 (ΔFx, ΔFy, ΔFz, ΔTx, ΔTy and ΔTz). That is, the outputdistribution matrix 24 calculates a command value ΔF4_1 for the positionadjusting mechanism 4_1, a command value ΔF4_2 for the positionadjusting mechanism 4_2 and a command value ΔF4_3 for the positionadjusting mechanism 4_3. Further, the output distribution matrix 24calculates a command value ΔF4_4 for the position adjusting mechanism4_4, a command value ΔF4_5 for the position adjusting mechanism 4_5 anda command value ΔF4_6 for the position adjusting mechanism 4_6.

Hereafter, the command values (ΔF4_1 to ΔF4_6) for the respectiveposition adjusting mechanisms 4 (4_1 to 4_6) are referred to as commandvalues 36 for the position adjusting mechanisms 4. The differencecalculator 27, the control compensator 23 and the output distributionmatrix 24 constitute a controller.

With the above-described configuration, the optical element positionapparatus of Embodiment 1 can perform positioning control for theoptical element 1.

However, the movement amounts 32 of the optical element 1 includemounting errors of the displacement sensor 6 and measurement errors ofthe displacement sensors 6, such as gain errors caused by measuringperformance. Therefore, in this state, as they are, the optical elementpositioning apparatus 7 fails to satisfy required positioning accuracy.Accordingly, it is necessary to calibrate the movement amounts 32 of theoptical element 1, which include measurement errors.

A calibration method of the optical element positioning apparatus 7 willbe described below.

The calibration of the optical element positioning apparatus 7 iscarried out using a calibrator 200. FIG. 7 schematically shows thecalibrator 200.

The optical element positioning apparatus 7 is mounted on the calibrator200, as shown in FIG. 7. A positioning mechanism 211 performspositioning of the base plate 5 in the optical element positioningapparatus 7 with respect to the calibrator 200.

The calibrator 200 is provided with displacement sensors 206 (206_X1,206_X2, 206_Y1, 206_Z1, 206_Z2, 206_Z3) that measure displacementamounts of the optical element 1. A displacement sensor superior to thedisplacement sensor 6 in measurement performance (gain error is smaller)is used as the displacement sensor 206.

The displacement sensor 206_X1 measures a displacement amount ΔX1 o ofthe optical element 1 in an X-axial direction with respect to thecalibrator 200. The displacement sensor 206_X2 measures a displacementamount ΔX2 o of the optical element 1 in the X-axial direction withrespect to the calibrator 200. The displacement sensor 206_Y1 measures adisplacement amount ΔY1 o of the optical element 1 in a Y-axialdirection with respect to the calibrator 200.

The displacement sensor 206_Z1 measures a displacement amount ΔZ1 o ofthe optical element 1 in a Z-axial direction with respect to thecalibrator 200. The displacement sensor 206_Z2 measures a displacementamount ΔZ2 o of the optical element 1 in the Z-axial direction withrespect to the calibrator 200. The displacement sensor 206_Z3 measures adisplacement amount ΔZ3 o of the optical element 1 in the Z-axialdirection with respect to the calibrator 200.

Hereafter, the measurement information (ΔX1 o, ΔX2 o, ΔY1 o, ΔZ1 o, ΔZ2o and ΔZ3 o) obtained by the displacement sensors 206 is referred to asmeasurement information 231 of the displacement sensor 206.

A movement amount transforming matrix 221, shown in FIG. 8, transformsthe measurement information 231 of the displacement sensors 206 intomovement amounts (ΔXo, ΔYo, ΔZo, Δθxo, Δθyo and Δθzo) of the controlcenter of the optical element 1 in the six-degrees-of-freedom of thecalibrator 200.

The movement amount transforming matrix 221 holds information on apositional relationship between the control center of the opticalelement 1 and the displacement sensors 206, as well as information on amounted angle of each displacement sensor 206. The information held bythe movement amount transforming matrix 221, such as the positionalrelationship between the control center of the optical element 1 and thedisplacement sensors 206, and the mounted angle of each displacementsensor 206, can be precisely obtained by using a tool, or the like,which is specially manufactured for the calibrator 200. Hereafter, themovement amounts (ΔXo, ΔYo, ΔZo, Δθxo, Δθyo and Δθzo) of the controlcenter of the optical element 1 in the six-degrees-of-freedom of thecalibrator 200 are referred to as movement amounts 232 of the opticalelement 1.

When the optical element positioning apparatus 7 is mounted on thecalibrator 200 to drive the optical element 1, the optical elementpositioning apparatus 7 can obtain the movement amounts 32 of theoptical element 1 in the six-degrees-of-freedom of the base plate 5 fromthe measurement information 31 of the displacement sensors 6. Thecalibrator 200 can obtain the movement amounts 232 of the opticalelement 1 in the six-degrees-of-freedom of the calibrator 200 from themeasurement information 231 of the displacement sensors 206.

The relationship between the movement amounts 232 of the optical element1 with respect to the calibrator 200 and the movement amounts 32 of theoptical element 1 with respect to the base plate 5 in the opticalelement positioning apparatus 7 can be expressed by a calibration matrix22, as shown in FIG. 10.

When the optical element 1 is moved in n-variations, n-sets of themovement amounts 32 of the optical element 1 with respect to the opticalelement positioning apparatus 7 can be obtained. The n-sets of themovement amounts 32 can be expressed as movement amount matrix 52, asshown in FIG. 11. Likewise, the n-sets of the movement amounts 232 ofthe optical element 1 with respect to the calibrator 200 can beobtained, and the n-sets of the movement amounts 232 can be expressed asa movement amount matrix 252, as shown in FIG. 11.

Referring to FIG. 11, multiplying both sides of the expression by aninverse matrix of the movement amount matrix 52 can calculate thecalibration matrix 22. To obtain the calibration matrix 22 forcalibrating in the six-degrees-of-freedom, the optical element 1 has tobe driven in at least six different positions and postures, and six ormore sets of the movement amounts 32 and six or more sets of themovement amount 232 have to be obtained.

FIG. 9 shows a positioning control method by the optical elementpositioning apparatus 7 when the calibration matrix 22 is used.

The measurement information 31 of the displacement sensors 6 istransformed into the movement amounts 32 of the optical element 1 in thesix-degrees-of-freedom in the orthogonal coordinate system by themovement amount transforming matrix (transformation processor) 21. Themovement amounts 32 of the optical element 1 are transformed intocalibrated movement amounts 43 (ΔXa, ΔYa, ΔZa, Δθxa, Δθya and Δθza) ofthe optical element 1 in the six-degrees-of-freedom by the calibrationmatrix (calibration processor) 22, the calibrated movement amounts 43being input into the difference calculator 27.

The difference calculator 27 calculates control deviations 44 (ErrXa,ErrYa, ErrZa, Errθxa, Errθya and Errθza) of the optical element 1 in thesix-degrees-of-freedom, as described below. That is, differences betweenthe calibrated movement amounts 43 (ΔXa, ΔYa, ΔZa, Δθxa, Δθya and Δθza)of the optical element 1 and the target movement amounts 30 (ΔXr, ΔYr,ΔZr, Δθxr, Δθyr and Δθzr) of the optical element 1 are calculated toobtain the control deviations 44.

The control compensator 23 includes a PI compensator or a PIDcompensator, a notch filter, a low-pass filter, and the like. Thecontrol compensator 23 calculates a driving force information 45 (ΔFxa,ΔFya, ΔFza, ΔTxa, ΔTya and ΔTza) of the optical element positioningapparatus 7 in the six-degrees-of-freedom, which are according to thecontrol deviations 44.

The output distribution matrix 24 holds the transforming matrix fortransforming the outputs from the position adjusting mechanisms 4 intothe movement amounts of the optical element 1 in thesix-degrees-of-freedom. The output distribution matrix 24 calculatescommand values 46 (ΔF4_1 a to ΔF4_6 a) for the position adjustingmechanisms 4 (4_1 to 4_6), based on the driving force information 45(ΔFxa, ΔFya, ΔFza, ΔTxa, ΔTya and ΔTza). As described above, thedifference calculator 27, the control compensator 23 and the outputdistribution matrix 24 constitute the controller.

Thus, calibrating the movement amounts 32 of the optical element 1 usingthe calibration matrix 22 can cause the optical element positioningapparatus 7 to perform more precise positioning control of the opticalelement 1.

Further, it is necessary to move the optical element 1 on the calibrator200 using the calibration matrix 22 to confirm whether or not themovement amounts of the optical element 1 (optical element positioningapparatus 7) satisfy a target accuracy. When the movement amountsthereof fail to satisfy the target accuracy, the calibration matrix 22has to be acquired again. FIG. 3 is a flowchart illustrating processesperformed by the calibrator 200 for acquiring the calibration matrix 22for the optical element positioning apparatus 7.

First of all, at step S101, the optical element positioning apparatus 7is mounted on the calibrator 200. At step S102, the optical elementpositioning apparatus 7 is driven to measure the movement amounts of theoptical element 1. At step S103, the calibration matrix 22 is acquired.Further, at step S104, the calibrator 200 causes the optical elementpositioning apparatus 7 to move the optical element 1 by using thecalibration matrix 22.

Then, at step S105, the calibrator 200 determines whether or not themovement amounts of the optical element 1 satisfy the target accuracy.When the target accuracy is not satisfied, the process returns to stepS102 and repeats steps S102 to S105. When the target accuracy issatisfied, the acquiring process of the calibration matrix 22 isterminated.

Next, a description will be made of a method to control wavefrontaberration of the projection optical system 101 within a permissiblevalue.

Fixing the base plates 5 of the respective optical element positioningapparatuses 7, which have been calibrated as described above, to theoptical element holding barrel 100, completes the assembly of theprojection optical system 101. However, when the base plates 5 of theoptical element positioning apparatuses 7 are fixed to the opticalelement holding barrel 100, mounting errors are generated unavoidably.Unless the positions of the base plates 5 are adjusted, the projectionoptical system 101 cannot correctly focus exposure light on a substrate.

Therefore, the projection optical system 101 is mounted on a wavefrontaberration measurement apparatus (not shown) and then, an adjustingmember, such as a spacer, is inserted between the base plate 5 and theoptical element holding barrel 100 until the wavefront aberration can bemeasured to adjust the position of the optical element positioningapparatuses 7.

Even when the positions of the optical element positioning apparatuses 7are only adjusted by using the adjusting member, the wavefrontaberration of the projection optical system 101 cannot be controlledwithin the permissible value. Therefore, the position of each opticalelement 1 is adjusted using the position adjusting mechanisms 4 in eachof the optical element positioning apparatuses 7. With this, thewavefront aberration of the projection optical system 101 can becontrolled within the permissible value.

It is preferable to use, as the displacement sensor 6 in the opticalelement positioning apparatus 7, a displacement sensor having anoriginal point and being capable of measuring an absolute displacementof the optical element 1 on the base plate 5. This enables measurementof the positions of the optical elements 1 (1_m1 to 1_m6), with respectto the base plate 5, when the wavefront aberration is controlled withinthe permissible value.

It is desired that the positions and angles of the optical elements 1(1_m1 to 1_m6), in the six-degrees-of-freedom when the wavefrontaberration is controlled within the permissible value, be stored in amemory (not shown) provided in the optical element positioningapparatuses 7 (7_m1 to 7_m6) or an exposure apparatus. Thisconfiguration can recreate a state in which the wavefront aberration ofthe projection optical system 101 is controlled within the permissiblevalue in a short time.

FIG. 4 is a flowchart showing an adjustment process to control thewavefront aberration of the projection optical system 101 within apermissible value. First of all, at step S201, each of the opticalelement positioning apparatuses 7 is fixed to the optical elementholding barrel 100. At step S202, the optical element holding barrel 100is mounted on the wavefront aberration measurement apparatus. At stepS203, the positions of the respective optical element positioningapparatuses 7 are adjusted using the adjusting members. At step S204,the wavefront aberration measurement apparatus measures the wavefrontaberration of the projection optical system 101.

At step S205, the wavefront aberration measurement apparatus determineswhether or not the wavefront aberration of the projection optical system101 can be measured. If not, the process returns to step S203, whereinthe positions of the optical element positioning apparatuses 7 areadjusted again using the adjusting members, and then, the processproceeds to step S204.

When the wavefront aberration can be measured, the process proceeds tostep S206, where the position adjusting mechanisms 4 of the opticalelement positioning apparatuses 7 are driven to adjust the position ofthe optical elements 1 (1_m1 to 1_m6) in directions in which thewavefront aberration is reduced.

Then, at step S207, the wavefront aberration of the projection opticalsystem 101, in which the positions of the optical elements 1 (1_m1 to1_m6) have been adjusted by driving the position adjusting mechanisms 4of the optical element positioning apparatuses 7, is measured. At stepS208, it is determined whether or not the measured wavefront aberrationis controlled within the permissible value. If not controlled within thepermissible value, the process returns to step S206, where the positionsof the optical elements 1 (1_m1 to 1_m6) are adjusted again by drivingthe position adjusting mechanisms 4 of the optical element positioningapparatuses 7 in directions in which the wavefront aberration isreduced, and then, the process proceeds to step S207.

When the wavefront aberration is controlled within the permissiblevalue, the process proceeds to step S209. At step S209, the positionsand angles of the optical elements 1 (1_m1 to 1_m6) in thesix-degrees-of-freedom are stored in the memory provided in the opticalelement positioning apparatuses 7 (7_m1 to 7_m6) or the exposureapparatus. Thus, the adjustment process is terminated.

In Embodiment 1, all the optical elements 1 (1 m_1 to 1 m_6) are drivenwith the optical element positioning apparatuses 7. However, some of theoptical elements 1 (1 m_1 to 1_m6) may be directly supported by (orfixed to) the base plate 5 with the holding mechanism 2.

Embodiment 2

The optical element positioning apparatus 7 described in Embodiment 1uses the displacement sensors 6 mounted on the base plate 5 to measurethe positions of the optical element 1 with respect to the base plate.

However, when the rigidity of the holding mechanism 2 is satisfactorilyhigh and thereby, the optical element 1 and the back plate 3 can beregarded as being integrally moved, as shown in FIG. 5, the displacementsensor 6 (6_X1, 6_Y1, 6_Y2, 6_Z1, 6_Z2, 6_Z3) may be mounted to the baseplate 5, to measure the displacement amounts of three points differentfrom each other on the back plate 3 in the Z axial direction, the Xaxial direction and the Y axial direction.

In this case, the positioning control of the optical element 1 may becarried out in the same manner as that in Embodiment 1, based on themeasurement results of the position of the back plate 3 with respect tothe base plate 5.

Embodiment 3

Next, an example of a projection exposure apparatus 300, in which aprojection optical system shown in the aforementioned Embodiments 1 and2 is provided, will be described, with reference to FIG. 12.

The exposure apparatus 300 of this embodiment uses EUV light asillumination light, for example, its wavelength is 13.5 nm, to exposeonto a substrate 340 as a wafer a circuit pattern formed on an exposuremask 320 by a step-and-scan method, a step-and-repeat method, or thelike. This exposure apparatus 300 is suitable for lithography processingin a size of less than a submicron or a quarter micron. Hereafter, thisembodiment will describe an exposure apparatus using the step-and-scanmethod, which is also referred to as a scanner, as an example.

The step-and-scan method is an exposure method in which continuousscanning of a wafer with respect to an exposure mask is performed, toexpose a pattern formed on the exposure mask onto the wafer, and thewafer is moved to a next exposure position by a stepped movement, aftereach shot of the exposure is completed. The step-and-repeat method is anexposure method in which a wafer is moved by a stepped movement afterevery one-shot exposure of the wafer, and then, the wafer is moved tonext exposure position.

Referring to FIG. 12, the exposure apparatus 300 includes anillumination apparatus 310 for illuminating the exposure mask 320 withlight from a light source, a mask stage 325 for mounting the mask 320,and a projection optical system 330 for introducing the light from theexposure mask 320 to the substrate (wafer) 340. It further includes awafer stage 345 for mounting the substrate 340, an alignment detectionmechanism 30, and a focus position detection mechanism 360.

FIG. 12 shows a catoptric reduction projection optical system includingfour mirrors between the exposure mask 320, at which the light isreflected and the substrate 340, which the light reaches after thereflection, to simplify the figure. However, six or more than sixmirrors are actually provided, as shown in Embodiments 1 and 2.

Further, as shown in FIG. 12, the EUV light has a low transmissivitywith respect to atmosphere, and it generates contamination by reactionwith residual gas (polymer organic gas, and the like). Thus, at least aninside of a path through which the EUV light passes, that is, an entireoptical system is kept in a vacuum atmosphere (VC).

The illumination apparatus 310 illuminates the exposure mask 320 withthe EUV light, for example, its wavelength is 13.4 nm, having an arcshape with respect to a view field having an arc shape of the projectionoptical system 330, and includes an EUV light source 312 and anillumination optical system 314.

The EUV light source 312 employs, for example, a laser plasma source. Inthe laser plasma source, a high-intensity pulse laser beam is irradiatedonto a target member in a vacuum container to generate high-temperatureplasma, which irradiates the EUV light, for example, its wavelength isapproximately 13 nm. The target member includes a metal layer, a gas jetand a liquid drop. In order to improve the average intensity of theirradiated EUV light, higher cyclic frequency of the pulse laser isdesirable, so that the EUV light source 312 is normally driven at acyclic frequency of several kHz.

The illumination optical system 314 is constituted by a condenser(collective) mirror 314 a and an optical integrator 314 b. The condensermirror 314 a collects the EUV light substantially isotopicallyirradiated from the laser plasma. The optical integrator 314 billuminates the exposure mask 320 uniformly with a predetermined NA.Further, the illumination optical system 314 is provided with anaperture 314 c for restraining an illumination region of the exposuremask 320 into an arc shape at a position conjugate with the exposuremask 320.

A cooling apparatus may be provided for cooling the condenser mirror 314a and an optical integrator 314 b, which are optical membersconstituting the illumination optical system 314. The cooling of thecondenser mirror 314 a and the optical integrator 314 b prevents theirdeformation caused by thermal expansions, thereby achieving goodimage-forming performance.

The exposure mask 320 is a reflective mask, and is formed thereon with acircuit pattern (or an image) to be transferred. The exposure mask 320is supported and driven by the mask stage 325. Diffracted light from theexposure mask 320 is reflected by the projection optical system 330described in Embodiments 1 and 2, and then, is projected onto thesubstrate 340. The exposure mask 320 and the substrate 340 are disposedin an optical conjugate relationship. Since the exposure apparatus 300employs the step-and-scan method, it projects a reduced pattern of theexposure mask 320 onto the substrate 340 by scanning the substrate 340with respect to the exposure mask 320.

The mask stage 325 supports the exposure mask 320, and is connected to atransferring mechanism (not shown). The mask stage 325 can employ anykinds of configurations. The transferring mechanism is constituted by alinear motor, or the like, and can move the exposure mask 320 by drivingthe mask 325 in at least an x-direction. The exposure apparatus 300relatively scans the exposure mask 320 and the substrate 340 in a statewhere they are synchronized.

The projection optical system 330 employs a plurality of mirrors 330 aformed of a multilayer film to reduce and to project the pattern on asurface of the exposure mask 320 onto the substrate 340, which is animage surface. The number of the plurality of mirrors 330 a is equal toor more than six, as described above. In order to realize a wideexposure region with as small a number of mirrors as possible, only anarrow region having an arc shape (field having a ring shape) locatedaway from the optical axis by a certain distance is used to transfer awide area by simultaneously scanning the exposure mask 320 and thesubstrate 340.

The mirrors 330 a may be cooled to prevent their deformation caused bythermal expansions by a cooling apparatus, thereby achieving goodimage-forming performance.

Although substrate 340 refers to a wafer in this embodiment, it widelyincludes a liquid substrate and other kinds of substrates. A photoresistis applied on the substrate 340.

The wafer stage 345 supports the substrate 340 with a wafer chuck 345 a.The wafer stage 345 moves the substrate 340 in the x, y and zdirections, using a linear motor, or the like. The exposure mask 320 andthe substrate 340 are synchronously scanned. The positions of the maskstage 325 and the wafer stage 345 are monitored by laserinterferometers, or the like, and both are driven at a certain velocityratio.

The alignment detection mechanism 350 measures a positional relationshipbetween the exposure mask 320 and an optical axis of the projectionoptical system 330, and that between the substrate 340 and the opticalaxis of the projection optical system 330. The positions of and an anglebetween the mask stage 325 and the wafer stage 345 are set such that theposition of a projected image of the exposure mask 320 coincides with apredetermined position on the substrate 340.

The focus position detection mechanism 360 measures a focus position ona surface of the substrate 340, and controls the position and the angleof the wafer stage 345, so as to always maintain the surface of thesubstrate 340 at a position where the image is formed through theprojection optical system 330 during exposure.

During exposure, the EUV light emerging from the illumination apparatus310 illuminates the exposure mask 320 to form the pattern on the surfaceof the exposure mask 320 onto a surface of the substrate 340. In thisembodiment, the image surface has an arc shape (having a ring shape).The exposure mask 320 and the substrate 340 are relatively scanned at aspeed ratio equivalent to a reduction magnification ratio to expose theentire surface of the mask 320.

Next, an embodiment of a method for manufacturing devices using theaforementioned exposure apparatus 300 will be described.

A device, such as a semiconductor integrated circuit element and aliquid crystal display element, is manufactured using theabove-mentioned exposure apparatus 300 through a step of exposing asubstrate, such as a wafer and a glass plate, on which aphotosensitizing agent is applied, a step of developing the exposedsubstrate, and other well-known steps.

According to the method for manufacturing the device of this embodiment,a device having a higher quality than that of conventional ones can bemanufactured.

The method for manufacturing the device using the exposure apparatus 300and also, the device itself, as a resultant product, constitute aspectsof the present invention.

While the present invention has been described with reference to variousembodiments, it is to be understood that the invention is not limited tothe disclosed exemplary embodiments. Rather, the scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall modifications, equivalent structures and functions.

For example, each of the aforementioned embodiments describes an opticalelement positioning apparatus used for a projection optical system in anexposure apparatus that uses EUV light as the exposure light. However,the optical element positioning apparatus can be used with exposureapparatuses that use exposure light other than the EUV light, such as anArF excimer laser and an F₂ laser.

1. An apparatus that includes an optical element and positions the optical element, the apparatus comprising: a holder configured to hold the optical element; a back plate configured to support the optical element via the holder; a mechanism configured to move the optical element in six-degrees-of-freedom; a base plate configured to support the back plate via the mechanism; three first displacement sensors disposed on the base plate and configured to measure respective displacement amounts of three mutually different points on the back plate in a first direction; a second displacement sensor disposed on the base plate and configured to measure a displacement amount of one point on the back plate in a second direction different from the first direction; two third displacement sensors disposed on the base plate and configured to measure respective displacement amounts of two mutually different points on the back plate in a third direction different from the first and second directions; a transformation processor configured to transform the six displacement amounts measured by the first, second and third displacement sensors into displacement amounts of the optical element in the six-degrees-of-freedom; a calibration processor configured to calibrate the displacement amounts transformed by the transformation processor with a calibration matrix, of which coefficients are previously obtained, to calibrate the displacement amounts in the six-degrees-of-freedom, which have errors due to measurement errors of the first, second and third displacement sensors; and a controller configured to output command values to the mechanism based on differences between the displacement amounts calibrated by the calibration processor and target displacement amounts of the optical element.
 2. A projection optical system comprising: the apparatus defined in claim 1; and a structure configured to support the apparatus.
 3. A projection optical system according to claim 2, further comprising a memory configured to store a position of the optical element in the six-degrees-of-freedom when a wavefront aberration of the projection optical system falls within a tolerance.
 4. An exposure apparatus comprising: a projection optical system defined in claim 2, wherein the exposure apparatus exposes a substrate to light via the projection optical system.
 5. A method of manufacturing a device, the method comprising: exposing a substrate to light using the exposure apparatus defined in claim 4; developing the exposed substrate; and processing the developed substrate to manufacture a device. 